Electrochemical devices realize an electric current from a change in one or more oxidation states during a chemical reaction. An electrochemical cell includes two types of electrodes—anodic and cathodic. An oxidation reaction occurs at the anodic electrode(s) while a reduction reaction occurs at the cathodic electrode(s).
A fuel driven electrochemical cell (hereinafter “fuel cell or fuel cells) is open system that consumes a fuel and oxygen source. Both are supplied to the fuel cell during its operation in which the fuel oxidizes at the anodic electrode(s) while at the same time the oxygen source reduces at the cathodic electrode(s). By regulating a supply of fuel and the oxygen source to a fuel cell, a user is able to controllably produce an electric current. Methanol, ethanol, and hydrogen are some examples of fuels usable in a fuel cell. Air and oxygen are some examples of oxygen sources usable in a fuel cell.
In a fuel cell having a proton conducting membrane (PCM), using hydrogen as the fuel, and air as the oxygen source, the hydrogen electrooxidizes at the anodic electrode(s) (diatomic hydrogen disassociates to protium [H2→2H°] and the protium in turn ionizes to generate one electron per proton [2H°→2H++2e-]). The protons are transported from the anodic electrode(s) to the cathodic electrode(s) through the proton conducting membrane (PCM) while the electrons are transported from the anodic electrode(s) to the cathodic electrode(s) along the external circuit via a load. Oxygen from the air reduces at the cathodic electrode(s) (e.g., diatomic oxygen converts to oxygen anions by four electrons discharged during oxidation of hydrogen [O2+4e-→2O2- (with a 2- charge)]). The product of reaction of protons and oxygen anions on the cathodic electrode(s) is water [2O2-+2H+→H2O]. An overall reaction (i.e., sum of half cell reactions at both types of electrodes) in a fuel cell with a proton conducting membrane theoretically produces current at a voltage very close to thermodynamic equilibrium voltage, that is, it operates at a voltage of about 1.23 V at 298 K. For decades, platinum (Pt) has been used as an electrocatalyst for the reduction of oxygen on the cathodic electrode(s) in hydrogen fuel cells. However, the reduction of oxygen at a Pt-cathodic electrode(s) occurs irreversibly that in turn causes high activation polarization losses that in turn significantly reduce fuel cell efficiency. There is a need for a new electrocatalyst having lower activation polarization losses while at the same time reducing cathodic electrode(s) platinum (Pt) content. Some alloys of Pt with transition metals (M) with an atomic ratio Pt/M=3:1 on activated carbon (hereinafter “Pt-M/C”) exhibit a specific catalyst activity (jk, IR-corrected) about 2.5 to about 3 times the specific catalyst activity (jk, IR-corrected) of elemental platinum (Pt) on activated carbon (hereinafter “Pt/C”). Yet such improved specific catalyst activity (jk, IR-corrected) is insufficient to justify a use of such fuel cells for automobile drive assemblies. It is estimated that at least 4-times higher specific catalyst activity (jk, IR-corrected) and mass activity (jm) with respect to Pt/C would be desirable in order for the fuel cells to be applicable in a commercial electric drive in automobiles. Detailed technical and economic parameters for cathodic electrode(s) electrocatalyst are set forth in B. Pivovar et al., “Applied Science for Electrode Cost, Performance, and Durability,” in the 2007 Progress Report for the US Department of Energy (DOE) Hydrogen Program (http ://www.hydrogen.energy.gov/pdfs/progress07/v_a—4_pivovar.pdf22 Apr. 2011).
GB2190537A discloses an electrocatalyst from a platinum-copper alloy containing 15 to 50 atomic percent (at %) copper (the balance being platinum) supported on a suitable substrate. These catalysts have enhanced activity and improved maintainability than previously known platinum electrocatalysts. According to one method, both platinum and copper are deposited simultaneously on activated carbon or another type of electrically conductive substrate from a mixture of platinum salt solution and copper salt solution. According to another method, first platinum is deposited from the platinum salt solution and then copper is deposited from the copper salt solution. Heat treating is carried out in a reducing atmosphere at temperatures ranging between 600° C. and 900° C. The maximum IR corrected specific catalyst activity (jk, IR-corrected) of these catalysts for the oxygen reduction reaction (ORR) is 0.108 mA/cmESA2 at 0.9 V vs. reversible hydrogen electrode (RHE).
US2009/0114061A1 and US2009/0098420A1 disclose a preparation of nanoparticles with a “core-shell” morphology using two-component alloys and three-component alloys of platinum and non-noble transition metals. In paragraphs [0027] to [0029], it is emphasized that the atomic ratio of platinum to non-noble (alkali) transition metals (Pt/M(alkali)) of the alloys is not limited. One method is strictly limited to the use of classic platinum catalysts on activated carbon (Pt/C) that are mixed with a previously prepared solution of copper or copper and cobalt salts (preferably nitrates). The resulting slurry is then frozen using liquid nitrogen and evacuated. The resulting powder containing Pt/C and alkali elements (Cu, Co) is then annealed in a muffle furnace between 200° C. and 1000° C. in an inert atmosphere. A catalyst thus obtained is then etched in an acid either prior to application to an electrode in a fuel cell or after the preparation of a membrane-electrode assembly. The alloy composition changes during etching as a considerable amount of non-noble metals (Cu and/or Co) is removed. After etching with an acid, all catalysts prepared according to US2009/0114061A1 and US2009/0098420A1 contained between 79 at % and 86 at % platinum with the balance being non-noble alkali transition metals. The maximum specific catalyst activity (jk, IR-corrected) and mass activity (jm) of a catalyst with an initial composition Pt25Cu75 mounted after etching and ionic exchange directly in the fuel cell at 0.9 V vs. RHE to 1.964 milliampere per square centimeter platinum (mA/cm2Pt) and 0.413 ampere per milligram platinum (A/mgPt). U.S. Pat. No. 7,700,521B2 discloses a preparation of electrocatalysts on the basis of nanoparticles of Pt—Cu alloys on electrically conductive substrates for application in anodic electrode(s) (oxidation) and cathodic electrode(s) (reduction) reactions for the production of electric current in fuel cells. Hydrogen or a hydrogen containing gas (e.g., methanol) is used as fuel and oxygen or air is used as oxidant. The catalyst alloy comprises 50 weight percent (wt %) to 80 wt % Pt.
U.S. Pat. No. 7,422,994B2 discloses a synthesis and preparation of electrocatalysts based on nanoparticles of Pt—Cu—W alloys and Pt—Cu—Ni alloys on electrically conductive substrates for use in anodic electrode(s) (oxidation) and cathodic electrode(s) (reduction) reactions in fuel cells. The catalyst alloy comprises 50 wt % to 80 wt % of Pt.
Thus, there exists a need for composition(s) and/or composite material(s) that provide improved catalytic activity with lower concentration of noble metals. Further, there exists a need for machine(s) and/or equipment including such composition(s) and/or composite(s). Furthermore, there exists a need for process(es) for synthesizing such composition(s) and/or composite(s).